1. Field of the Invention
This invention relates to casing stabbing apparatus employed for the purpose of mechanically engaging large diameter heavy well casing of the type used in oil and gas wells.
2. Brief Description of the Prior Art
In the production of hydrocarbons from subterranean locations, it is a prevalent practice to case the well bore, with the casing first being lowered into position in the well bore from a rig rotary table, and then cemented in position in the well bore. In deep wells of the type currently within the capability of the technology (exceeding 15,000 feet), it is often necessary to use casing having a diameter which is quite large. Sections of casing having diameters of 14 inches and above become quite heavy and pose a number of problems in handling, particularly in connecting and disconnecting the casing sections to each other, and in lowering the casing string into the well bore. The bulk and weight of the large diameter casing sections also pose severe problems of safety to rig crews installing the casing, and require the utilization of mechanical assistance wherever feasible.
Various types of mechanical arrangements have been employed for handling tubular goods utilized in oil and gas production, including drill pipe and casing. The roughnecks on the rig floor are in no case relieved of all necessity to handle the pipe, and these personnel remain subject to bruises incurred by accidental body contact with swinging pipe, and occasionally death is caused by accidental blows to the head inflicted by the heavy swinging tubular sections. In at least the case of tripping in and out of wells (the terms refer to the process of connecting and disconnecting pipe sections in running drill pipe or casing into or out of the well bore), it is necessary to manually handle the pipe for purposes of alignment as the threaded end sections of the drill pipe or casing are joined to each other.
In the joinder of casing, it is the customary practice to suspend one section of casing from the rotary table in the rig floor, with the lower end portion of the section projecting into the well bore and the threaded upper end portion exposed above the rotary table. An elongated section of casing to be connected to the section which is suspended in the well bore is picked up by the tackle carried in the mast of the derrick, and is hung from a crown block so as to be suspended vertically over the subjacent section (hanging from the rotary table) to which it is to be connected.
After the following section of casing to be joined to the section hung from the rotary table has been brought over the rotary table with the crown block, it is necessary to precisely align the threaded end section, termed the pin, with the female threaded end section (the box) of the casing section therebelow. This is accomplished by one or two roughnecks standing on the well floor and another member of the rig crew standing on a platform midway between the rig floor and the top of the derrick The man who stands on the platform must grasp the casing section and prevent it from oscillating as it is slowly lowered by the crown block to a position where the threads carried at its lower end are immediately above and ready to be threadedly joined with the female threads in the section therebelow. The man aloft on the platform helps to guide the casing section to the precise position where, as it is further lowered, the male threads will mate with the female threads of the section hung from the rotary table.
Although some systems have been provided for mechanically racking various types of drill pipe and casing as it is pulled from the well bore and racked during a trip out of the well bore, and systems also devised for aligning and connecting sections of drill pipe, the advent of drilling to depths in excess of 15,000 feet has resulted in the utilization of large diameter casing which is very heavy, and which requires very husky crewmen, particularly the person who must stand aloft on the platform and damp the oscillations of the swinging casing section, and see that it is lowered in precise alignment with the section to which it is to be joined. This process, called stabbing, is repeated many times as hundreds of sections of casing are joined to each other and lowered into the well bore. The task of casing stabbing is very fatiguing to the personnel who manually handle the heavy tubular elements, and even without the lack of alertness caused by fatigue after hours of working at these jobs, there is always danger to the personnel from severe injury resulting from being struck by the swinging casing sections.
Among mechanical systems which have previously been proposed for handling various types of tubular goods employed in the drilling of oil and gas wells, one example is to be found in the disclosure of U.S. Pat. No. 1,812,351 to Marsh. In this patent, a pipe racking device is depicted and described which utilizes a pair of angulated piston and cylinder assemblies to swing drill pipe from its position over the rotary table to the desired racked position in the corner of the derrick as the stand of pipe is unscrewed from the drill string being removed from the well. A hook and clamp assembly carried at the end of the two piston and cylinder assemblies is used for surrounding and tightly engaging the drill pipe section once it has been disconnected from the string therebelow, and the piston and cylinder subassemblies are then energized to swing the drill pipe section over to the racking position. The piston and cylinders used in this system are located relatively close to the derrick floor and are counterbalanced to extend in a horizontal position by weights acting through flexible members extended over pulleys and attached at one end to each of the piston and cylinder subassemblies.
Another mechanical device for centering casing during the drilling of oil and gas wells is that which is depicted in Russe U.S. Pat. No. 4,295,527. In the Russe patent, a pair of tongs are provided which are hydraulically converged to clamp about a casing section at one location therealong. These tongs are rigidly aligned by a mechanical connecting member with a split sleeve element joinable to the top of the section of casing therebelow into which the superjacent suspended casing section gripped by the tongs is to be stabbed. A set of conventional power tongs is then used to spin up the upper casing section so that the threads are tightly engaged and the joint made up.
Another type of pipe stabbing guide is illustrated and described in Bolpin U.S. Pat. No. 2,147,002. The entire Bolpin assembly is located relatively close to the rig floor, and is a two part device, with one part gripping the end portion of the descending casing section and the other attached to the upper end of that section of the casing string which is suspended in the rotary table. The two parts are interconnected by a vertically extending stem.
The Bolpin patent includes a good description of the difficulty posed to the drilling crew in quickly and accurately swinging the new section of casing or drill pipe into position for joinder to the drill string suspended in the well bore.
In the Bolpin stabbing guide, the element which actually guides the upper section of drill pipe is merely a finger against which this section of drill pipe is abutted or rested as it descends to the point where the male threads at the lower end thereof make contact with and engage the female threads in the box section carried on the upper end of the pipe section therebelow. No positive retentive engagement of the finger with the upper section of pipe is provided.
Other types of stabbing devices and guides are shown in Graham et al. U.S. Pat. No. 2,206,184, Calhoun U.S. Pat. No. 2,450,934, True U.S. Pat. No. 2,828,024, Scaggs U.S. Pat. No. 4,274,777, Guier U.S. Pat. No. 3,533,516 and Moise U.S. Pat. No. 2,184,051.
The Moise patent employs a pair of hydraulic piston and cylinder assemblies extended from two adjacent corners of the derrick so as to be generally at right angles to each other with the free ends of the piston rods carrying elements which can push against a well casing section to cooperatively (as between the two pushing elements) bring the casing into a vertical position in which it is aligned for stabbing into the casing section therebelow. The casing is not, however, retentively clamped or physically surrounded by the guiding structure during its use.